Proton-liberation accompanying succinoxidase activity in vesicles reconstituted from soluble components resembles the process in uncoupled native membranes. both amount to about 5% of the value in coupled membranes, they require an unperturbed membrane, and sufficient potassium to neutralize membrane potential. Assays for membrane potential and DeltapH using flow dialysis can lead to erroneous overestimations of the potential and underestimation of DeltapH when these values are below 100mV.